Respiration

The circulatory system carries glucose, oxygen and carbon dioxide around the body in the bloodstream.

The glucose needed for respiration derives from digestive breakdown of foods.

The oxygen comes from air breathed into the lungs. Carbon dioxide is breathed out.

All cells are near the thin blood capillaries which supply glucose from gut and oxygen from lungs, that diffuse into the cells, and the waste carbon dioxide diffuses out to be transported to the lungs.

Aerobic respiration is respiration using oxygen. It is the most efficient way to release energy from glucose.

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration:

The bigger the concentration difference, the steeper the diffusion gradient and the faster the rate of diffusion.